It’s a surprisingly simple but important question in medicine. While a body temperature of 98.6°F (37°C) is generally considered “normal,” this number doesn’t account for temperature differences between individuals — and even within individuals at various times of the day. While a common sign of infection, fever can also occur with other medical conditions, including autoimmune and autoinflammatory diseases.

“Many factors come together to set an individual’s ‘normal’ temperature, such as age, size, time of day and maybe even ancestry,” says Jared Hawkins, MMSc, PhD, the director of informatics for Boston Children’s Hospital’s Innovation & Digital Health Accelerator (IDHA) and a member of the hospital’s Computational Health Informatics Program. “We want to help create a better understanding of the normal temperature variations throughout the day, to learn to use fever as a tool to improve medical diagnosis, and to evaluate the effect of fever medications on symptoms and disease course.”

That’s where Feverprints comes in — a free app developed by IDHA and the Autoinflammatory Diseases Clinic at Boston Children’s to capture temperature data from the public. By leveraging ResearchKit, Apple’s open source software framework, the Feverprints team can gather frequent, accurate data shared from people’s iPhones (iPhone 5, iPhone 6) or the latest generation of the iPod Touch. (Unfortunately, Android users won’t be able to participate.)

After downloading the Feverprints app, adults (and children with parental consent) who join the study will be regularly reminded to record their temperature (using any type of thermometer) and answer questions about their symptoms, medications, lifestyle and health. The data will be anonymized and logged in a secure database. All participants will receive a summary of their data and can share it with their doctors.

The Boston Children’s team — led by Fatma Dedeoglu, MD, director of the Autoinflammatory Diseases Clinic, and rheumatologist Jonathan Hausmann, MD — will mine these crowdsourced data to refine the range of body temperatures called normal and febrile. They will also use the data to define unique patterns of temperature — “feverprints” — that could help clinicians diagnose infections and other diseases more quickly and accurately.

Last but not least, the team will systematically examine how effectively fever-reducing medicines work to reduce temperature in real-world use.

Feverprints is Boston Children’s second ResearchKit app. The first, C-Tracker, was launched in 2015 to gather information about the real-world impacts of hepatitis C and drive improvements in treatment.